1. Field of the Invention
The present invention relates to a multilayer capacitor capable of greatly reducing the equivalent serial inductance (EBL) and capable of controling the equivalent serial resistance (ESR).
2. Description of the Related Art
In recent years, the central processing units (CPUs) used for data processing apparatuses have remarkably increased in operating frequency due to higher processing speeds and higher integration. On the other hand, reduction of the power consumption has resulted in a remarkably reduction in the operating voltages.
Therefore, in power sources for supplying power to CPUs, there are sharp, large fluctuations due to the load current. It has become extremely difficult to keep fluctuations in the voltage accompanying this to within tolerances of the power source.
Therefore, sometimes a decoupling capacitor is connected in parallel between the power source and CPU. A conventional decoupling capacitor is comprised of a two-terminal structure multilayer ceramic capacitor. At the time of a transient fluctuation in the quickly changeable load current, current in supplied from this multilayer ceramic capacitor to the CPU or other integrated circuit by quick charging and discharging to suppress fluctuation of the power source voltage and stabilize the power source.
Note that in a conventional multilayer ceramic capacitor able to be used for a decoupling capacitor, the internal conductors connected to the external terminal electrodes are stacked via ceramic layers. The directions of currents flowing through the internal conductors have therefore been the same.
Along with the increasingly higher operating frequencies of today""s CPUs, however the fluctuations in the load current have become faster and larger. Therefore, the parasitic part of the ESL of the multilayer ceramic capacitor itself obstructs the charge and the discharge, so that it effects on fluctuations of the power source voltage. The effect due to the multilayer ceramic capacitor is therefore becoming insufficient.
That is, in a conventional multilayer ceramic capacitor, since the ESL is high, fluctuation of the power source voltage V easily becomes greater in the same way as above along with fluctuations at the time of charging and discharging accompanying fluctuations in the load current 1. This is because the fluctuations in voltage at the time of transition of the load current are approximated by the following equation 1 and therefore the level of the ESL is related to the magnitude of fluctuation of the power source voltage. Further, from equation 1, reduction in the ESL can be said to be linked with stabilization of the power source voltage.
dv=ESLxc2x7di/dtxe2x80x83xe2x80x83(1)
where, dV is transitory fluctuation of voltage (V),
i is the fluctuation of current (A), and
t is the tire of fluctuation (sec)
Further, in a multilayer ceramic capacitor, the ESR is smaller and the high frequency characteristics are better than with an electrolytic capacitor, but advances in materials technology and thick film forming technologies have lad to remarkable advances in reducing the thickness of layers of dielectrics and increasing the number of layers in recant years. As a result, large capacity multilayer ceramic capacitors having large electrostatic capacities comparable with those of aluminum electrolytic capacitors and tantalum electrolytic capacitors have been appearing.
Further, the much greater number of layers of multilayer ceramic capacitors in recent years has not only increased the electrostatic capacity, but also caused a tendency for a further drop in the ESR. That is, the ESR at the time of high frequency fluctuation of the current is predominately due to the electrical resistance of the internal conductors, so when the greater number of layers causes an increase in the density of the internal conductors of the multilayer ceramic capacitor, the ESR is further reduced.
That is, in the equivalent circuit of the multilayer ceramic capacitor, the equivalent resistance of the internal conductors themselves laminated via the ceramic layers are formed at both sides of the capacitor circuit. When the greater number of layers causes an increase in the capacitance of the capacitor circuit, the whole resistance decreases and the ESR is further reduced in inverse proportion to the number of layers.
On the other hand, a large capacity capacitor is mainly used for flattening the output of a switching power source. If using a capacitor with a small ESR, however, while this is effective for reducing the output ripple voltage, when the ESR is overly small, the control system of the switching power source suffers from unstable output voltage or a susceptibility to abnormal oscillation. This in because when using a capacitor with an overly small ESR, the phase easily becomes delayed in the feedback circuit of the control circuit and the control circuit can no longer function normally.
Therefore, in the past, for applications such as flattening the output of the switching power source, often an electrolytic capacitor having a large ESR is used instead of a multilayer capacitor.
As opposed to this, from the standpoints of reducing costs and reducing size, it is desirable to use a multilayer capacitor for such applications as well. A further increase in layers of the multilayer capacitor in pursuit of greater capacity in the future, however, may invite a greater reduction in the ESR and therefore an overly small ESR.
A first object of the present invention is to provide a multilayer electronic device able to greatly reduce the ESL.
A second object of the present invention is to produce a multilayer capacitor able to be used for various applications by controling the ESR.
To attain the first object, according to a first aspect of the present invention, there is provided a multilayer capacitor comprising at least two of a first internal conductor and a second internal conductor formed in flat shapes, at least two of a first polarity conductor and a second polarity conductor formed in flat shapes, a dielectric body formed by stacking a plurality of dielectric sheets with dielectric sheets sandwiching each of the conductors, a first terminal electrode arranged at an outside of the dielectric body so as to be able to be connected to an external circuit and connected to the first internal conductor, a second terminal electrode arranged at the outside of the dielectric body so as to be able to be connected to the external circuit and connected to the second internal conductor, a first linkage electrode for connecting the first internal conductor and the first polarity conductor at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along a stacking direction become opposite to each other, and a second linkage electrode for connecting the first internal conductor and the first polarity conductor at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along the stacking direction become opposite to each other.
According to the multilayer capacitor according to the first aspect of the present invention, the dielectric body is formed by stacking a plurality of dielectric sheets with each dielectric sheet sandwiched between two first and second internal conductors and two types of first and second polarity conductors formed in flat shapes. Two first and second terminal electrodes arranged at the outside of the dielectric body so as to enable connection to an external circuit are connected to the first and second internal conductors.
The first internal conductor and first polarity electrode are connected by a first linkage electrode and become the same polarity. Further, the second internal conductor and second polarity electrode are connected by a second linkage electrode and become the own polarity. Further, portions where the directions of the current become opposite between these conductors adjoining each other along the stacking direction are created.
Therefore, there is the action that the magnetic fields are canceled out at locations where the currents flow in opposite directions. Along with this, there is the effect that the parasitic inductance of the multilayer capacitor itself can be made smaller and the ESL can be reduced.
Due to this, according to the multilayer capacitor of the first aspect of the present invention, the ESL can be greatly reduced. Therefore, this multilayer capacitor can be suitably used as a decoupling capacitor for a power source of a CPU and for example the oscillation of the power source voltage can be suppressed.
In the first aspect of the present invention, preferably the first internal conductor is formed with a first linkage lead part for connecting with the first linkage electrode separate from a first terminal lead part for connecting with the first terminal electrode, the second internal conductor is formed with a second linkage lead part for connecting with the second linkage electrode separate from a second terminal lead part for connecting with the second terminal electrode, the first polarity conductor is formed with a third linkage lead part for connecting with the first linkage electrode, and the second polarity conductor is formed with a fourth linkage lead part for connecting with the second linkage electrode. By forming these lead parts, the electrical connections between the internal conductors and the terminal electrodes or linkage electrodes become more reliable.
In the first aspect of the present invention, alternatively the second polarity conductor is arranged between the first internal conductor and the first polarity conductor through the electric sheets, and the first polarity conductor is arranged between the second polarity conductor and the second internal conductor. By arranging the elements in this way, it become easy to create portions where the directions of currents between conductors adjoining each other in the stacking direction become opposite.
In the first aspect of the present invention, preferably a plurality of the first and second internal conductors and the first and second polarity conductors are ford in the stacking direction through the dielectric sheets. By stacking a plurality of such conductors, not only is the electrostatic capacity of the capacitor increased, but also the action of canceling out the magnetic fields in further enhanced, the parasitic inductance of the multilayer capacitor itself can be further reduced, and the ESL can be further reduced.
To achieve the first object of the invention, in accordance with a second aspect of the present invention, there is provided a multilayer capacitor having at least two of a first internal conductor and second internal conductor formed in flat shapes, a plurality of first polarity conductors formed in flat shapes, a plurality of second polarity conductors formed in flat shapes, a dielectric body formed by stacking a plurality of dielectric sheets with dielectric sheets sandwiching each of the conductors, a first terminal electrode arranged at an outside of the dielectric body so as to enable connection to an external circuit and connected to the first internal conductor, a second terminal electrode arranged at the outside of the dielectric body so as to enable connection to the external circuit and connected to the second internal conductor, a first linkage electrode for connecting the first internal conductor and one of the first polarity conductors at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along a stacking direction become opposite to each other, a second linkage electrode for connecting the second internal conductor and one of the second polarity conductors at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along the stacking direction become opposite to each other, a first intermediate linkage electrode for connecting the first polarity conductors at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along the stacking direction become opposite to each other, and a second intermediate linkage electrode for connecting the second polarity conductors at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along the stacking direction become opposite to each other.
In the multilayer capacitor of the second aspect of the present invention as well, actions and effects similar to those of the multilayer capacitor according to the first aspect of the present invention can be expected. Further, in the second aspect of the present invention, it is possible to increase the number of the first and second polarity electrodes connected to the first and second internal conductors. Further, it is possible to increase the number of the linkage electrodes. Further, it is possible to make the directions of currents flowing through adjoining linkage electrodes opposite to each other. As a result, the action of canceling out the magnetic fields is further enhanced, the parasitic inductance of the multilayer capacitor itself can be further reduced, and the ESL can be further reduced.
In the second aspect of the present invention, preferably the first internal conductor, the second internal conductor, the first polarity conductors, and the second polarity conductors are formed with lead parts for connection with any of the first terminal electrode, second terminal electrode, first linkage electrode, second linkage electrode, first intermediate linkage electrode, and/or second intermediate linkage electrode.
By forming these lead parts, connection between the conductors end electrodes becomes easier and it becomes easier to create portions where the directions of currents between conductors adjoining each other along the stacking direction become opposite to each other.
In the second aspect of the present invention, preferably at least one of the first internal conductor and second internal conductor is comprised of at least two split conductors insulated from each other on the same flat surface, and these split conductors are connected to a wide first linkage electrode wide or second linkage electrode.
By using such a broad first linkage electrode or second linkage electrode, it is possible to form at least one of the first internal conductor and second internal conductor by at least two split conductors insulated from each other on the same flat surface. In this case as well, it becomes easier to create portions where the directions of currents between conductors adjoining each other along the stacking direction become opposite to each other.
To achieve the second objects according to a third aspect of the present invention, there is provided a multilayer capacitor comprising a dielectric body formed by stacking dielectric layers, at least one pair of a first terminal electrode and second terminal electrode arranged at an outside of the dielectric body and able to be connected to an external circuit, a first internal conductor arranged in a flat shape inside the dielectric body and connected to the first terminal electrode, a second internal conductor arranged in a flat shape inside the dielectric body so as not to be connected to the first internal conductor and connected to the second terminal electrode, at least one first polarity conductor arranged inside the dielectric body while being separated from the first internal conductor and the second internal conductor by the dielectric layers, and a first linkage electrode arranged at the outside of the dielectric body and connecting the first internal conductor and the first polarity conductor.
In the multilayer capacitor of the third aspect of the present invention, the first internal conductor is connected to the first polarity conductor through the first linkage electrode. These conductors function as the same polarity. Therefore, as the path through which the current flows inside the multilayer capacitor becomes longer, the ESR of the multilayer capacitor increases.
Therefore, this multilayer capacitor can be used even for applications of flattening the output of the switching power source instead of an electrolytic capacitor and therefore the number of layers can be increased and the capacity can be made much larger. That is, this multilayer capacitor is increased in the ESR, so can suppress oscillation of voltage of the power source and can be used for various applications such as a switching power source.
In the third aspect of the present invention, preferably the capacitor further has, separate from the first polarity conductor, a second polarity conductor arranged inside the dielectric body while being separated from the first internal conductor and the second internal conductor by the dielectric layers, and a second linkage electrode connecting the second internal conductor and the second polarity conductor is formed at the outside of the dielectric body.
In this case, a conductor of the same polarity is connected to not only the first internal conductor, but also the second internal conductor. Therefore, as the path through which the current flows inside the multilayer capacitor becomes longer, the ESR of the multilayer capacitor increases.
In the third aspect of the present invention, preferably the first internal conductor is formed with a first terminal lead part for connection with the first terminal electrode and is formed with a first linkage lead part for connection with the first linkage electrode. By formation of the lead parts, the connections between the first internal conductor and the terminal electrode and linkage electrode become more reliable.
In the third aspect of the prevent invention, preferably the second internal conductor in formed with a second terminal lead part for connection with the second terminal electrode and is formed with a second linkage lead part for connection with the second linkage electrode. By formation of the lead parts, the connections between the second internal conductor and the terminal electrode and linkage electrode become more reliable.
In the third aspect of the present invention, preferably the first polarity conductor is formed with a third linkage lead part for connection with the first linkage electrode. By formation of the lead part, the connection between the first polarity conductor and first linkage electrode becomes more reliable.
In the third aspect of the present invention, preferably the second polarity conductor is formed with a fourth linkage lead part for connection with the second linkage electrode. By formation of the lead part, the connection between the second polarity conductor and second linkage electrode becomes more reliable.
In the third aspect of the present invention, preferably a plurality of the first internal conductors and second internal conductors are formed inside the dielectric body. By increasing the number of layers of the first internal conductor and second internal conductor, the electrostatic capacity of the capacitor increases. Further, in the third aspect of the present invention, since the first polarity conductor is connected to at least the first internal conductor, it is possible to control the ESR to a desired value by suitably adjusting the number of layers of the first internal conductor and second internal conductor.
In the third aspect of the present invention, preferably a notch formed in the first internal conductor and/or second internal conductor. By forming a notch, the path of the current at that notch becomes longer, the conductor width becomes narrower, the resistance increases, and the effect of increase of the ESR in large.
In the third aspect of the present invention, preferably the first internal conductor and the first polarity conductor are connected by a plurality of the first linkage electrodes. By connecting the first internal conductor and first polarity conductor by a plurality of first linkage electrodes, the connections between the conductors become more reliable and it is possible to effectively prevent poor connections etc.
In the third aspect of the present invention, preferably a plurality of the first terminal electrodes and a plurality of the second terminal electrodes are provided at the outside of the dielectric body, the first internal conductor is formed with a plurality of first terminal lead parts for connection to the plurality of first terminal electrodes, and the second internal conductor is formed with a plurality of second terminal lead parts for connection to the plurality of second terminal electrodes.
In this case, since a plurality of terminal electrodes is provided, it is possible to realize a multilayer capacitor. Further, it is possible to realize the actions and effects of the third aspect of the present invention. Note that in the multilayer capacitor, the adjoining terminal electrodes become opposite in polarity.
In the third aspect of the present invention, preferably the width of at least part of the first internal conductor other than at the first terminal lead part is narrower than the width of the first terminal lead part. In this case as well, since the width of the conductor through which the current passes becomes narrower, the resistance increases and the ESL can be increased.
To achieve the first and second objects, according to a fourth aspect of the present invention, there is provided a multilayer capacitor comprising a dielectric body formed by stacking dielectric sheets, a pair of a first terminal electrode and second terminal electrode arranged at an outside of the dielectric body and insulated from each other, at least one first linkage electrode arranged at the outside of the dielectric body and insulated from the first terminal electrode and second terminal electrode, a first internal electrode stacked inside the dielectric body through the dielectric sheets and connected to the first terminal electrode, a second internal electrode stacked inside the dielectric body through the dielectric sheets and connected to the second terminal electrode, and a first polarity conductor stacked inside the dielectric body through the dielectric sheets, connected to the first linkage electrode so as to be connected to the first internal electrode.
In the multilayer capacitor of the fourth aspect of the present invention, it is possible to achieve the actions and effects of the multilayer capacitors of the first to third aspects of the present invention.